172 THE ANATOMY OF THE HORSE. 



fibres pass transversely inwards, the most superior getting inserted into 

 the body and glossal process of the hyoid bone, and the others into a 

 median fibrous raphe between the two muscles. The muscle is to be 

 left intact at present, and its attachments will be better seen in the 

 dissection of the mouth. 



Action. — To raise the body of the tongue towards the roof of the 

 mouth, and thus assist in mastication and deglutition. 



Nerve to the mylo-hyoid and inferior belly of the digastric. This 

 is a branch of the inferior maxillary division of the 5th cranial nerve. 

 It descends between the internal pterygoid muscle and the vertical ramus ; 

 and passing above the upper edge of the mylo-hyoid, it nins do\rawards 

 on the surface of that muscle, in company with the submental artery. 

 In part of its course it is covered by the lower belly of the digastricus, 

 and it sends to that muscle a distinct branch, which enters it on its 

 outer side. 



the appendages of the eye. 



These are — the eyelids, the membrana nictitans, the caruncula 

 lachrymalis, the conjunctival membrane, and the lachrymal apparatus. 

 The lachrymal gland — the most important part of the last mentioned 

 apparatus— will be dissected with the interior of the orbit; but the 

 other structures enumerated are to be examined now. 



The Eyelids. The front of the eye is protected by two movable cur- 

 tains — the upper and lower eyelids ; and at the inner side of the eye there 

 is placed another structure — the membrana nictitans, which plays the 

 part of a third eyelid. The upper lid is larger than the lower, and has 

 a greater range of movement. Each ej'^elid presents two surfaces, two 

 borders, and two extremities. The outer or fecial surface is formed by 

 a continuation of the skin, and is covered by short hairs. Among these 

 there occur in the lower lid some long tactile bristles. The inner or ocular 

 surface is lined by the conjunctival membrane, and is moulded on the 

 front of the eye. If the upper lid be everted there will be found on its 

 inner surface, near the outer angle, a number of minute openings, into 

 which bristles should be passed. These are the openings of the 

 excretory ducts of the lachrymal gland. On the same surface, but near 

 the opposite angle, and close to the free edge of each lid, there is a 

 round opening of larger size, but still minute. These are the puncta 

 lachrymalia, the orifices of the lachrymal ducts, by which the lachrymal 

 secretion is conveyed away from the eye. The free borders of the eyelids 

 circumscribe the palpebral fissure, which is a mere line when the eye is 

 closed, but is ovoid or elliptical, with the long axis directed obliquely 

 upwards and outwards, when the e^^e is open. The free edge of each lid 

 is somewhat stiff", this stiffiiess being due to a slender rod of cartilage 

 which extends along it. The meibomian glands are lodged in depressions 

 on the ocular surface of this cartilage, and may be seen through the 



